DEERFIELD, Ill. — Both the strong incidence of influenza and the rise in the number of flu shots administered in December positively impacted comparable prescriptions filled at Walgreens on a day-fall adjusted basis, the company reported Friday. Flu shots administered at pharmacies and clinics season-to-date were nearly 5.5 million versus approximately 5.3 million last year, the retailer noted.

December 2012 had one additional Sunday and Monday and one fewer Thursday and Friday compared with December 2011, negatively impacting prescriptions filled in comparable stores by 230 basis points. DFA prescriptions filled at comparable stores were positively impacted by 140 basis points due to the higher incidence of flu in this year’s December and 70 basis points due to more flu shots administered in the month.

Prescriptions filled at comparable stores decreased by 2.3% in December and were flat on a day-fall adjusted basis.

Walgreens reported December sales of $6.7 billion, a decrease of 4% as compared to the same month in fiscal 2012.

December pharmacy sales decreased 4.9%, while comparable store pharmacy sales decreased 8.9% and by a day-fall adjusted 6.6%. DFA comparable store pharmacy sales were negatively impacted by 570 basis points due to generic drug introductions in the last 12 months. Pharmacy sales accounted for 56.7% of total sales for the month.